1. Field of the Invention
The present invention relates to a code division multiple access (CDMA) system, and more particularly to controlling power in a CDMA system using antenna diversity.
2. Description of the Background Art
In a CDMA mobile communication system, such as a cellular mobile communication system or a personal communication service system, the transmission power of a mobile station (or personal station) must be appropriately controlled because of a propagation attenuation resulting from a multipath fading. Also, because the strength of a signal received from a base station is varied according to a distance from the base station, the power control of the mobile station must also be performed to correct the signal strength.
If the base station utilizes an extremely high transmission signal power, the entire system capacity is reduced due to an interference of the mobile station with other mobile stations. On the contrary, if the base station utilizes an extremely low transmission signal power, the mobile station cannot demodulate a desired signal, resulting in a reduction in performance such as a degradation in voice quality or a loss in data.
Thus, the mobile station measures the power of a signal received from the base station, compare the measured power with a reference value and generates a power control command signal in response to the compared result. The mobile station inserts the generated power control command signal to a data signal and transmits the resultant signal to the base station. The base station extracts the power control command signal from a signal received from the mobile station and adjusts its transmission signal power based upon the extracted power control signal, which is known as a closed loop power control.
In the above power control in the CDMA system, the demultiplexed data at a transmitting stage of the base station are transmitted through corresponding antennas utilizing a transition diversity. The transmitted data are received at a receiving stage of the mobile station under different channel environments. However, the receiving stage of the mobile station controls the signals transmitted through the respective antennas with the same power regardless of the fact that they are transmitted under the different channel environments.